Electrophotographic elements containing soluble cyclic sulfone electron transport agents

ABSTRACT

A sulfone charge transport agent and a multilayered electrophotographic element in which at least one of said layers includes polymeric binder and the sulfone charge transport agent. The general structure of the charge transport agent is:   &lt;IMAGE&gt;   R is alkyl or cycloalkyl having from 1 to about 10 carbons, or aryl or heteroaryl having a total of carbons and heteroatoms of from 6 to about 12. T is alkyl having from 1 to 4 carbons.

FIELD OF THE INVENTION

This invention relates to electrophotography, electrophotographicelements and cyclic sulfone compounds and more particularly relates toelectron transport agents that are derivatives of4H-thiopyran-1,1-dioxide which exhibit improved solubility and toelectrophotographic elements that include those agents.

BACKGROUND OF THE INVENTION

In electrophotography an image comprising a pattern of electrostaticpotential (also referred to as an electrostatic latent image), is formedon a surface of an electrophotographic element comprising at least twolayers: an insulative photoconductive layer and an electricallyconductive substrate. The electrostatic latent image can be formed by avariety of means, for example, by imagewise radiation-induced dischargeof a uniform potential previously formed on the surface. Typically, theelectrostatic latent image is then developed into a toner image bycontacting the latent image with an electrographic developer. Ifdesired, the latent image can be transferred to another surface beforedevelopment.

The imagewise discharge is brought about by the radiation-inducedgeneration of electron-hole pairs, by a material (often referred to as acharge-generation material) in the electrophotographic element.Depending upon the polarity of the initially uniform electrostaticpotential and the type of materials in the electrophotographic element,either the holes or the electrons that have been generated migratetoward the charged surface in the exposed areas and cause the imagewisedischarge of the initial potential. What remains is a non-uniformpotential constituting the electrostatic latent image.Electrophotographic elements often have separate layers that can beidentified as a charge generation layer (CGL) and a charge transportlayer (CTL) on the basis of their primary functions.

Many electrophotographic elements are designed to be initially chargedwith a negative polarity. They contain material, known as ahole-transport agent, which facilitates the migration of positive holestoward the negatively charged surface in imagewise exposed areas. Apositively charged toner is used to develop the unexposed areas. Becauseof the wide use of negatively charging elements, many types ofpositively charging toners are available.

For some applications, however, it is desirable to develop the exposedrather than the unexposed surface areas of the element. For example, inlaser printing of alphanumeric characters it is more desirable to exposethe small surface area that will form visible alphanumeric toner images,rather than waste energy exposing the large background area. In order toaccomplish this with available high quality positively charging toners,it is necessary to use an electrophotographic element that is designedto be positively charged. Positive toner can then develop the exposedsurface areas (which will have relatively negative electrostaticpotential).

An electrophotographic element designed to be initially positivelycharged should contain an electron-transport agent, that is, a materialwhich facilitates the migration of photogenerated electrons toward thepositively charged surface. Unfortunately, while many goodhole-transport agents are available, relatively few electron transportagents are known and many prior art compounds have one or moredrawbacks.

In order for electron transport to occur in the CTL, two events arenecessary. The first event is the capture of the electron injected bythe CGL. The second event is the movement of electrons from one moleculeto the next in the CTL. The former process affects the quantum yield forelectron capture as measured in terms of electrophotographic speed underconditions of low-intensity continuous exposure, while the latterprocess represents the kinetics of electron exchange in the CTL asmeasured in terms of mobility.

Some previous electron-transport agents do not perform the electrontransporting function well except under limited conditions or in limitedtypes of electrophotographic elements. Some agents cause an undesirablyhigh rate of discharge of the electrophotographic element before it isexposed, also referred to as high dark decay.

Some previous electron-transport compounds have limited solubility ordispersibility in coating solvents and limited compatibility inpolymeric binders. Increasing the concentration of an electron-transportagent in a polymeric layer, in the absence of phase-separation,increases the electron-transport mobility of the layer; accordingly,photogenerated electrons move through the layer at a higher velocity andtraverse the layer in a shorter period of time. The higher the mobility,the shorter is the waiting period between exposure and development, andthe greater is the number of copies that can be made in a given amountof time. Even when sufficient amounts of electron-transport agent can becompatibly incorporated in an electrophotographic element duringmanufacture, problems can arise during use due to migration of theelectron transport agent.

Among electron-transport materials, those molecules based on1,1-dioxo-4H-4-(dicyanomethylidene) thiapyran-4-one (the "sulfones")have electron mobilities and electrophotographic speeds that are highrelative to most electron-transport materials. U.S. Pat. Nos. 4,514,481to Scozzafava et al; and 4,968,813; 5,013,849; 5,034,293; and 5,039,585all to Rule et al; teach derivatives of 4H-thiopyran-1,1-dioxides. U.S.Pat. No. 4,514,481 discloses4-dicyanomethylene-2,6-diphenyl-4H-thiopyran-1,1-dioxide (also referredto herein as DPS), which has the structural formula: ##STR2##

U.S. Pat. No. 5,039,585 discloses4-dicyanomethylene-2-p-tolyl-6-phenyl-4H-thiopyran-1,1-dioxide (alsoreferred to herein as PTS), which has the structural formula: ##STR3##DPS and PTS have about the same electron mobilities, however, PTS ismore soluble.

The terms "solubility" and "compatibility" are used herein to describethe ability of a first material to disperse in a second material so asto form a homogenous blend. The term "solubility" is generally used todescribe the ability of a material to dissolve in liquid solvents toform a solution. The term "solubility" used herein, does not, however,exclude dispersions which appear to be homogeneous, at least tounmagnified examination. The term "compatibility" is generally used todescribe the ability of a material to blend with a polymer so as toproduce a material which appears to be homogeneous, at least tounmagnified examination. The term "miscibility" defines a similarconcept. The terms "incompatible" and "incompatibility" and the like,used herein refer to an intermixture which is characterized bysegregation of sulfone and polymer binder, that is, crystallization oraggregate formation which is visible without magnification. Suchcrystallization or aggregate formation causes such problems asundesirable dark decay, as well as scatter or absorption of actinicradiation intended to pass through the charge-transport layer.

U.S. Pat. No. 4,514,481 describes the incorporation of DPS and othersimilar sulfones in polymeric binder layers of electrophotographicelements at a concentration of 30% by weight (based upon the totalweight of the agent and the binder) for good performance. The upperlimit of compatibility (solubility or homogeneous dispersibility) ofcompounds such as DPS in many polymeric binders is about 40% by weight.At such concentrations, DPS and similar sulfones are on the edge ofincompatibility and an elevation in temperature can cause migrationwithin the binder and the formation of undesirable crystallineaggregates. This is a major shortcoming, since electrophotographicelements encounter elevated temperatures during normal use in a copier.PTS has a higher solubility than DPS in solvents useful for preparing aphotoconductor. This allows higher loading levels in the finalphotoconductor composite, which in turn results in increasedphotogenerated charge migration, leading to potentially fasterphotodischarge speeds and lower toe/erase voltages. PTS has acompatibility limit of about 60% by weight. At that loading level, PTShas crystallization problems comparable to the problems seen with DPS at40% loading.

Thus, there is a need for electrophotographic elements containingelectron transport agents which have good electron mobilities andelectrophotographic speeds and exhibit good solubility in coatingsolvents and good compatibility with polymeric film-forming binders andthus can be used at very high loading levels.

SUMMARY OF THE INVENTION

The invention, in its broader aspects, provides a sulfone chargetransport agent and a multilayered electrophotographic element in whichat least one of said layers includes polymeric binder and the sulfonecharge transport agent. The general structure of the charge transportagent is: ##STR4## R is alkyl or cycloalkyl having from 1 to about 10carbons, or aryl or heteroaryl having a total of carbons and heteroatomsof from 6 to about 12. T is alkyl having from 1 to 4 carbons.

It is an advantageous effect of at least some of the embodiments of theinvention that the sulfones of the invention have both unexpectedly goodcompatibility with polymeric binders and solubility in solvents forthose binders, and good electron-transport properties inelectrophotographic elements of the invention.

DESCRIPTION OF PARTICULAR EMBODIMENTS

The electrophotographic elements of the invention have at least onelayer that includes one or more of the sulfones of the invention, ascharge transport agent. The sulfones of the invention have both goodelectron mobilities and good solubility in coating solvents andcompatibility with film-forming polymeric binders. In particularembodiments of the invention, disclosed in detail herein, the electronmobility of the sulfone of the invention is about the same as that ofPTS and the solubility in coating solvents and compatibility withpolymer binders are higher than for PTS. As is shown by the examplesbelow, in the sulfones of the invention, and such other sulfones as PTS,there is an empirical correlation between compatibility of a sulfonewith a polymer binder and solubility of the sulfone in a solvent forthat polymer binder. The high solubility and compatibility of thesulfones of the invention presents advantages, at high charge transportagent loading levels; both during manufacture of an electrophotographicelement, in ease of use of coating solutions; and during use of theelement, in increased photogenerated charge migration, which can lead tofaster photodischarge speeds and lower toe/erase voltages.

The sulfones of the invention have the general structure: ##STR5## T isalkyl having from 1 to 4 carbons. R is alkyl or cycloalkyl having from 1to about 10 carbons; aralkyl or heteroaralkyl having a from 1 to about 4carbon alkene moiety and a five or six membered aromatic orheteroaromatic ring; or aryl or heteroaryl having a total of carbons andheteroatoms of from 6 to about 12. The backbone or ring system of R canbe unsubstituted or can be substituted by alkyl having from 1 to about12 carbons, alkoxy having from 1 to about 12 carbons, nitro, cyano,dialkylamino, arylalkylamino, and diarylamino.

In a preferred embodiment of the invention, R is an aromatic orheteroaromatic ring system having a single ring or two linked or fusedrings. Suitable aliphatic R groups include: methyl, ethyl, propyl,isopropyl, butyl, isobutyl, t-butyl, pentyl, hexyl, 2-ethylhexyl,cyclopentyl, cyclohexyl, 4-methylcyclohexyl, and octyl. Suitable aralkylgroups include: benzyl and phenethyl. Suitable aromatic andheteroaromatic R groups include: phenyl, naphthyl, 2-thienyl, 3-thienyl,2-furyl, 5-methyl-2-thienyl, and 2-selenophene. Examples of specificsulfones of the invention are: ##STR6##

The sulfones of the invention, can be prepared from1,5-disubstituted-1,4-pentadiyn-3-ones by the following scheme: ##STR7##A route to 1,5-disubstituted-1,4-pentadiyn-3-ones is described by Dettyet al., J. Org. Chem., 1987, Vol. 52, p. 3662. The reaction ofsubstituted 1,4-pentadiyn-3-ones with sodium hydrosulfide to produce1-thiopyran-4-ones is described by Detty et al., Tetrahedron, (1985),Vol. 41, pp. 4853-4859. Conversion of thiopyranones to the corresponding1,1-dioxides by oxidizing agents such as peracetic acid and reaction ofthe dioxides with malonitrile under basic conditions are disclosed inU.S. Pat. No. 4,514,481, which is hereby incorporated herein byreference.

The substituted 1,4-pentadiyn-3-ones required to prepare theelectron-transport agents of the invention can be synthesized by thereaction of alkyl-, aralkyl-, or cycloalkyl-substituted alkynyl lithiumcompounds with aryl-substituted propargyl aldehydes to yield1,4-pentadiyn-3-ols, which are then oxidized by reagents such as chromicacid to the corresponding diynones. This is illustrated by the followingscheme: ##STR8##

Phenylpropargyl aldehyde is commercially available. Other substitutedpropargyl aldehydes can be prepared via propiolic esters fromtetrachlorocyclopropene and an arene according to the following scheme:##STR9##

The reduction of propiolic esters to propargyl alcohols can be effectedby hydride reducing agents, for example, diisobutylaluminum hydride. Foroxidation of propargyl alcohols to the corresponding aldehydes,pyridinium chlorochromate is a suitable reagent.

The reaction scheme previously described is best suited for thepreparation of 6-alkyl-2-aryl sulfones. For 2,6-diaryl sulfones and2-heteroaryl-6-aryl sulfones, the following reaction scheme ispreferred: ##STR10##

Similar approaches to DPS and PTS have been described in Chen, et al, J.Org. Chem., Vol. 51, (1986) p. 3282; and U.S. Pat. No. 4,514,481 toScozzafava et al; and U.S. Pat. No. 5,039,585 to Rule et al. Thestarting material having the general structure: ##STR11## can beproduced by condensation of a 4-alkyl benzaldehyde with excess acetone.

The new electrophotographic elements of the invention can be of varioustypes, all of which contain one or more of the sulfones of the inventionas electron-transport agents in one or more layers of the elements. Thevarious types of elements in accordance with the present inventioninclude both those commonly referred to as single layer orsingle-active-layer elements and those commonly referred to asmultiactive, or multi-active-layer elements. All of theelectrophotographic elements of the invention have multiple layers,since each element has at least an electrically conductive layer and oneother layer.

Single-active-layer elements are so named because they contain only onelayer that is active both to generate and to transport charges inresponse to exposure to actinic radiation. Such elements have anadditional electrically conductive layer in electrical contact with thephotoconductive layer. In single-active-layer elements of the invention,the photoconductive layer contains a charge-generation material togenerate electron/hole pairs in response to actinic radiation and anelectron-transport material, comprising one or more of the sulfones ofthe invention, which is capable of accepting electrons generated by thecharge-generation material and transporting them through the layer toeffect discharge of the initially uniform electrostatic potential. Thephotoconductive layers of single-active-layer electrophotographicelements usually contain from about 0.01 to 50 weight percent ofcharge-generating material. The photoconductive layer is electricallyinsulative except when exposed to actinic radiation. The photoconductivelayer can contain an electrically insulative polymeric film-formingbinder which is itself the charge-generating material. Alternatively,the photoconductive layer contains both a charge generating material anda polymeric binder that is not charge-generating. In either case, theelectron-transport agent, the sulfone of the invention, is dissolved ordispersed as uniformly as possible in the photoconductive layer.

Multiactive layer elements are so named because they contain at leasttwo active layers, at least one of which is capable of generatingcharge, that is, electron/hole pairs, in response to exposure to actinicradiation and is therefore referred to as a charge-generation layer(CGL), and at least one of which is capable of accepting andtransporting charges generated by the charge-generation layer and istherefore referred to as a charge-transport layer (CTL). Such elementstypically comprise at least an electrically conductive layer, a CGL, anda CTL. Either the CGL or the CTL is in electrical contact with both theelectrically conductive layer and the remaining CTL or CGL. The CGLcontains a charge-generation material. If the charge-generation materialis not also a polymeric binder, then a polymeric binder can also bepresent. The CTL contains a charge-transport agent, which is the sulfoneof the invention, and a polymeric binder.

Single-active-layer and multiactive layer electrophotographic elementsand their preparation and use in general, are well known and aredescribed in more detail, for example, in U.S. Pat. Nos. 4,701,396;4,666,802; 4,578,334; 4,719,163; 4,175,960; 4,514,481 and 3,615,414, thedisclosures of which are incorporated herein by reference.

In preparing the electrophotographic elements of the invention, thecomponents of the photoconductive layer (in single-active-layerelements) or CTL (in multiactive layer elements), including any desiredaddenda, are dissolved or dispersed together in a liquid and then coatedover an appropriate underlayer. The underlayer can be an electricallyconductive layer, or support or, with a multiactive layer element, theCGL. The liquid is then allowed or caused to evaporate from the mixtureto form the permanent photoconductive layer or CTL. The weight percentof charge transport agent in the completed photoconductive layer or CTLdoes not differ substantially from the weight percent of the chargetransport agent in the total of polymer binder and sulfone present inthe coating solution.

The ratio of charge transport agent to binder or of charge-transportagent and charge generation material to binder can be varied widely,depending on the particular materials employed. In theelectrophotographic elements of the invention, useful results can beobtained when the amount of active charge transport agent or chargegeneration material or both contained within a layer is greater thanabout 10 weight percent and less than about 90 weight percent. (Thepercentage of charge generating material will vary if thecharge-generating material is also the binder.) In many uses a desirableminimum concentration of charge transport agent is about 20 weightpercent and an even better minimum concentration is about 40 weightpercent. A desirable maximum concentration is well below the upper limitof compatibility seen during preparation of the electrophotographicelement. The reason is that during use, the maximum limit ofcompatibility effectively drops. For example, a desirable range for theconcentration of PTS in an electrophotographic element is about 40 to 50weight percent; since an element having more than 50 weight percent PTScan exhibit zones of incompatibility, i.e., crystallinity, aftermoderate electrophotographic use. An electrophotographic element havinga sulfone of the invention, rather than PTS, has much greatercompatibility and is thus more resistant to crystallization. Thus, apreferred range of concentration for the sulfone: ##STR12## in anelectrophotographic element of the invention, is from 40 to 70 weightpercent and a preferred range of concentration of the sulfone: ##STR13##is from 40 to 60 weight percent.

The polymeric binder in the layer containing the sulfone of theinvention is a film-forming polymer that preferably also has goodelectrically insulating properties. The film forming characteristics ofthe polymer can present a practical limit on the amount of sulfone thatcan be present in the CTL or photoconductive layer. Too high aconcentration of sulfone may cause the layer to be excessively soft orfriable making it unusable. Binder polymers should provide little or nointerference with the transport; and in single active layer elements,the generation; of charges in the layer. The binder polymer can also beselected to provide additional functions. For example, adhering thesulfone containing layer to an adjacent layer; or, as a top layer,providing a smooth, easy to clean, wear-resistant surface. Examples ofsuitable polymeric binders include: styrene-butadiene copolymers;vinyltoluene-styrene copolymers; styrene-alkyd resins; silicone-alkydresins; soya-alkyd resins; vinylidene chloride-vinyl chloridecopolymers; poly(vinylidene chloride); vinylidene chloride-acrylonitrilecopolymers; vinyl acetate-vinyl chloride copolymers; poly(vinylacetals), such as poly(vinyl butyral); nitrated polystyrene;poly(methylstyrene); isobutylene polymers; polyesters, such aspoly[ethylene-co-alkylenebis(alkyleneoxyaryl) phenylenedicarboxylate];phenol-formaldehyde resins; ketone resins; polyamides; polycarbonates;polythiocarbonates; poly-[ethylene-co-isopropylidene-2,2-bis(ethyleneoxy-phenylene)terephthalate]; copolymers of vinyl haloacrylatesand vinyl acetate; chlorinated polyolefins such as chlorinatedpolyethylene; and polyimides, such aspoly[1,1,3-trimethyl-3-(4'-phenyl)-5-indane pyromellitimide]. Examplesof binder polymers which are particularly desirable from the viewpointof minimizing interference with the generation or transport of chargesinclude: bisphenol A polycarbonates and polyesters such aspoly[(4,4'-norbornylidene)diphenylene terephthalate-co-azelate].

The choice of a polymeric binder, to some extent defines the choices ofsolvent to be used in preparing the sulfone containing layer. Thesulfone and binder must both be soluble in the solvent and the solventmust have acceptable characteristics relative to any underlayer. Thesolvent, for example, should not dissolve away the underlayer and shouldprovide for good bonding between the two layers. Health and safetyconcerns and convenience are additional considerations. Included amongmany useful solvents for this purpose are, for example, aromatichydrocarbons such as benzene, toluene, xylene and mesitylene; ketonessuch as acetone and butanone; halogenated hydrocarbons such asdichloromethane, trichloroethane, chloroform, and ethylene chloride;ethers, including ethyl ether and cyclic ethers such as tetrahydrofuran,other solvents such as acetonitrile; and mixtures thereof.

The polymeric binders useful for the sulfone containing layer can alsobe used in producing a CGL. Any charge-generation material can beutilized in elements of the invention. Such materials include inorganicand organic (including monomeric organic, metallo-organic and polymericorganic) materials, for example, zinc oxide, lead oxide, selenium, orphthalocyanine, perylene, arylamine, polyarylalkane, and polycarbazolematerials, among many others.

CGL's and CTL's in elements of the invention can optionally containother addenda such as leveling agents, surfactants, plasticizers,sensitizers, contrast control agents, and release agents, as is wellknown in the art.

Various electrically conductive layers or supports can be employed inelectrophotographic elements of the invention, for example, paper (at arelative humidity above 20 percent) aluminum-paper laminates; metalfoils such as aluminum foil, zinc foil, etc.; metal plates such asaluminum, copper, zinc, brass and galvanized plates; vapor depositedmetal layers such as silver, chromium, vanadium, gold, nickel, aluminumand the like; and semiconductive layers such as cuprous iodide andindium tin oxide. The metal or semiconductive layers can be coated onpaper or conventional photographic film bases such as poly(ethyleneterephthalate), cellulose acetate, polystyrene, etc. Such conductingmaterials as chromium, nickel, etc. can be vacuum-deposited ontransparent film supports in sufficiently thin layers to allowelectrophotographic elements so prepared to be exposed from either side.

Electrophotographic elements of the invention can include various, asoptional layers, any of the additional layers known to be useful inelectrophotographic elements in general, for example, subbing layers,overcoat layers, barrier layers, and screening layers.

The following preparations and examples are presented to furtherillustrate some specific electrophotographic elements of the inventionand chemical compounds useful as electron-transport agents therein.Melting points were determined on a Thomas-Hoover melting pointapparatus and are uncorrected. ¹ H NMR spectra were recorded either on aGeneral Electric QE-300 spectrometer or on a Varian Gemini-200spectrometer. UV-visible-near infrared spectra were recorded on aPerkin-Elmer Lambda 9 spectrophotometer. Infrared spectra were recordedon a Beckman IR 4250 instrument or a Perkin-Elmer 298 infraredspectrophotometer. Microanalyses were performed on a Perkin-Elmer 240 C,H, and N Analyzer.

EXAMPLE 1

The procedures given below and in Example 2 are representative of thoseused to prepare the sulfones of the invention.

Preparation ofE,E-1-(p-isoproplphenyl)-5-(2-thienyl)-1,4-pentadine-3-one:

A mixture of 7.9 grams (0.042 mol) ofE-4-(p-isopropylphenyl)-3-butene-2-one, 4.7 grams (0.042 mol) of2-thiophene carboxaldehyde, 2 mL of 10% sodium hydroxide, 30 mL ofwater, and 75 mL of ethanol was stirred at ambient temperature for 15hours. The product was collected by filtration and air dried to give10.2 grams (86% of theoretical yield) ofE,E-1-(p-isopropylphenyl)-5-(2-thienyl)-l,4-pentadien-3-one as a yellowsolid. Melting point was determined to be 100°-101° C. Proton nuclearmagnetic resonance (¹ H NMR) was conducted in CDCl₃ : d 7.84 (d, 1H,J=16 Hz), 7.69 (d, 1H, J=16 Hz) , 7.53 (AA'BB', 2H) , 7.39 (m, 1H) ,7.32 (m, 1H), 7.25 (AA'BB', 2H) , 7.06 (dxd, 1H, J= 3.6, 5 Hz), 6.96 (d,1H, J=16 Hz), 6.87 (d, 1H, J=16 Hz), 2.90 (septet, 1H, J=7 Hz), 1.23 (d,6H, J=7 Hz). Infrared spectroscopy was conducted using a KBr pellet:2960, 1650, 1585, 1180, and 705 cm⁻¹. Field desorption mass spectralanalysis (FDMS) was consistent with the proposed formula (C₁₈ H₁₈ OS) m⁺/z 316.

Preparation of2,3,5,6-Tetrahydro-2-(p-isopropylphenyl)-6-(2-thienyl)thiapyran-4-one:

A solution of 35.0 grams (0.124 mol) ofE,E,-1-(p-isopropylphenyl)-5-(2-thienyl)-1,4-pentadien-3-one, 8 grams ofsodium acetate, and 400 mL of ethanol was heated on a steam bath in aflask equipped with mechanical stirring, water-cooled reflux condenser,and gas inlet tube. Hydrogen sulfide gas was slowly bubbled into thereaction mixture until the pentadienone was consumed. The reactionmixture was cooled to ambient temperature and was diluted with 2 litersof water. The aqueous phase was extracted with dichloromethane 4 timesusing 300 mL each time. The combined organic extracts were washed withbrine, dried over magnesium sulfate, and concentrated. The solid residue(35 grams, 90% of theoretical yield), believed to represent a mixture ofdiastereomers, was used without further purification. FDMS wasconsistent with the proposed formula (C₁₈ H₂₀ OS₂) m⁺ /z 316.

Preparation of1,1-Dioxo-2,3,5,6-tetrahydro-2-(p-isopropylphenyl)-6-(2-thienyl)thiapyran-4-one:

30% Peracetic acid (120 mL) was added dropwise to a solution of2,3,5,6-tetrahydro-2-(p-isopropylphenyl)-6-(2-thienyl)thiapyran-4-one(35.0 grams, 0.111 mol) and 8 grams of anhydrous sodium acetate in 300mL of dichloromethane. After addition was complete, the reaction mixturewas stirred for 1 hour at ambient temperature and was then diluted with500 mL of water. The organic phase was separated and the aqueous phasewas extracted with an additional 300 mL of dichloromethane. The combinedorganic extracts were washed with dilute sodium hydroxide solution,dried over magnesium sulfate, and concentrated to give 30.0 grams (80%of theoretical yield) of an oily residue that was used without furtherpurification. ¹ H NMR (CDCl₃) was: d 7.50-7.00 (m, 7H) , [4.86 (dxd),4.74 (t){1 H}], 4,52 (m, 1H), 3.8-2.8 (m, 5H), 1.23 (d, 6H, J=7 Hz).FDMS was consistent with (C₁₈ H₂₀ O₃ S₂): m⁺ /z 348.

Preparation of4H-1,1-Dioxo-2-(p-isopropylphenyl)-6-(2-thienyl)thiapyran-4-one:

A solution of 25.0g (0.0718 mol) of1,1-dioxo-2,3,5,6-tetrahydro-2-(p-isopropylphenyl)-6-(-2-thienyl)thiapyran,130 mL of dimethylsulfoxide, 3.0 grams of iodine, and 2 mL ofconcentrated sulfuric acid was heated on a steam bath with mechanicalstirring for 4 hours. The reaction mixture was cooled to ambienttemperature and was diluted with 1 liter of water. The products wereextracted with dichloromethane 4 times, using 200 mL each time. Thecombined organic extracts were washed with brine, dried over magnesiumsulfate, and concentrated. The residue was slurried with ethanol and theresulting solid was collected by filtration and dried to give 20.0 grams(81% of theoretical yield) of a dark solid. Melting point was determinedto be 92.0°-93.5° C. 1^(H) NMR (CDCl₃) was: d 7.95 (dxd, 1H, J=1, 4 Hz),7.54 (AA'BB', 2H), 7.61 (dxd, 1H, J=1, 5 Hz), 3.54 (AA'BB', 2H), 7.20(dxd, 1H, J=4, 5 Hz), 6.74 (d, 1H, J=2.7 Hz), 6.67 (d, 1H, J=2.7 Hz),2.96 (septet, 1H, J=7 Hz), 1.27 (d, 6H, J=7 Hz). IR (KBr) was: 2960,1680, 1585, 1415, 1305, 1135 and 710 cm⁻¹. FDMS was consistent with (C₁₈H₁₆ O₃ S₂) : m⁺ /z 344. Elemental analysis found C=62.42; H=4.74. Thiscompares to calculated values for C₁₈ H₁₆ O₃ S₂ of C=62.77; H=4.68.

Preparation of4H-1,1-Dioxo-2-(p-isopropylphenyl)-6-(2-thienyl)-4-(dicyanomethyl-idene)thiapyran:

A mixture of 19.1 grams (0.0555 mol) of4H-1,1-dioxo-2-(p-isopropylphenyl)-6-(2-thienyl)thiapyran-4-one and 7.5grams (0.114 mol) of malononitrile in 160 mL of ethanol was heated atreflux with mechanical stirring. To this solution, a solution of 0.50 mLof piperidine in 40 mL of ethanol was added dropwise via pressureequalizing addition funnel. After 4 hours at reflux, the reactionmixture was cooled to ambient temperature. The crystalline solid wascollected by filtration and washed with 100 mL of ethanol. The solid washeated to boiling in ethyl acetate/ethanol and filtered to provide 12.0grams (55% of theoretical yield) of a burnt-orange crystalline solid.Melting point=199°-201° C. 1H NMR (CDCl₃) was: d 7.99 (dxd, 1H, J=1, 4Hz), 7.78 (AA'BB', 2H), 7.67 (dxd, 1H, J=1, 5 Hz), 7.37 (AA'BB', 2H),7.32 (d, 1H, J=2.6 Hz), 7.26 (d, 1H, J=2.6 Hz), 7.225 (dxd, 1H, J=4, 5Hz), 2.97 (septet, 1H, J=7 Hz), 1.27 (d, 6H, J=7 Hz); IR (KBr) 2225,1305, and 1135 cm⁻¹. FDMS was consistent with (C₂₁ H₁₆ N₂ O₂ S₂): m⁺ /z392. Elemental analysis found: C=64.26; H=4.16; N=7.19. This compares tocalculated values for C₂₁ H₁₆ N₂ O₂ S2 of C=64.26; H=4.11; N=7.14.

Saturated solutions of the sulfone of this example were prepared intoluene and dichloromethane at ambient temperature (approx. 23° C.) todetermine maximum solubility. Results are presented in Table 1.

EXAMPLE 2

The following procedures were followed:

Preparation of E,E-1-(p-isopropylphenyl)-5-phenyl-1,4-pentadien-3-one:

A mixture of 81.0 grams (0.555 mol) trans-4-phenyl-3-buten-2-one, 81.7grams (0.552 mol) 4-isopropylbenzaldehyde, 12 mL of 10% sodiumhydroxide, 150 mL water and 220 mL ethanol was stirred at ambienttemperature for 15 hours. The crystalline product was collected byvacuum filtration to give 90.0 grams (59% of theoretical yield) ofE,E-1-(p-isopropylphenyl)-5-phenyl-1,4-pentadien-3-one as a yellowsolid. Melting point=76.0°-78.0° C. IR (KBr) 2960, 1655, 1595, 1345,1195, 980, 820, 760, 695 cm⁻¹ ; FDMS, m⁺ /z 276 (C₂₀ H₂ O). ¹ H NMR(CDCl₃) d 7.74 (d, 2H, J=16 Hz), 7.59 (m, 2H) , 7.55 (d, 2H, J=8 Hz) ,7.39 (m, 3H) , 7.26 (d, 2H, J=8 Hz), 7.09 (d, 1H, J=16 Hz), 7.045 (d,1H, J=16 Hz), 2.93 (septet, 1,H, J=7 Hz), 1.26 (d, 6H, J=7 Hz). Anal.Calcd. for C₂₀ H₂₀ O; C, 86.92;H, 7.29. Found: C, 86.87,H, 7.32.

Preparation of2,3,5,6-Tetrahydro-2-(p-isopropylphenyl)-6-phenylthiopyran-4-one:

A solution of 90.0 grams (0.326 mol) ofE,E,-1-(p-isopropylphenyl)-5-phenyl-l,4-pentadien-3-one, 15.0 ganhydrous, sodium acetate, 200 mL ethanol and 50 mL dimethylformamidewas heated on a steam bath in a flask equipped with a mechanicalstirring device, a water-cooled reflux condenser and a gas inlet tube.Hydrogen sulfide gas was slowly bubbled into the reaction mixture untilthe pentadienone was consumed. The reaction mixture was cooled toambient temperature and diluted with 1 L water. The aqueous phase wasextracted with dichloromethane (4×125 mL). The combined organic extractswere dried over magnesium sulfate and concentrated. The resulting oilyresidue (90.0 g 89% of theoretical yield), a mixture of diastereomers,was used without further purification. FDMS, m⁺ /z 310 (C₂₀ H₂₂ OS). ¹ HNMR (CDCl₃) d 7.1-7.5 (m, 9H), 4.3 (m, 2H), 2.95 (m, 5H), 1.25 (d, 6H,J=7 Hz.)

Preparation of1,1-Dioxo-2,3,5,6-tetrahydro-2-(p-isopropylphenyl)-6-phenylthiapyran-4-one:

32% Peracetic acid (125 mL) was added dropwise with frequent stirring toa solution of2,3,5,6-Tetrahydro-2-(p-isopropylphenyl)-6-phenylthiapyran- 4-one (90.0grams, 0.290 mol) and 15.0 grams of anhydrous, sodium acetate in 350 mLdichloromethane. After addition was complete, the reaction mixture wasstirred for 1 hour at ambient temperature and then diluted with 1 Lwater. The aqueous phase was neutralized with a 10% solution of sodiumhydroxide and solid sodium bicarbonate. The organic phase was separatedand the aqueous phase was extracted with an additional 250 mL ofdichloromethane. The combined organic extracts were dried over magnesiumsulfate and concentrated to give 90.0 grams (91% of theoretical yield)of an oily residue that was used without further purification. FDMS, m⁺/z 342 (C₂₀ H₂₂ O₃ S) . ¹ H NMR (CDCl₃) d 7.0-7.5 (m, 9H), 4.5 (m, 1H),3.72 (m, 1H), 2.9 (m, 5H), 1.25 (d, 6H, J=7 Hz).

Preparation of4H-1,1-Dioxe-2-(p-isopropylphenyl)-6-phenylthiapyran-4-one:

A solution of 90.0 grams (0.263 mol) of1,1-Dioxo-2,3,5,6-tetrahydro-2-(p-isopropylphenyl)-6-phenylthiapyran-4-one,110 mL methyl sulfoxide, 3.0 grams of iodine and 2.0 mL of concentratedsulfuric acid was heated on a steam bath for 4 hours. The reactionmixture was cooled to ambient temperature and diluted with 1 L water.The aqueous phase was neutralized with a 10% solution of sodiumhydroxide and the organic phase was extracted into dichloromethane(4×125 mL). The combined organic extracts were dried over magnesiumsulfate and concentrated to an oily residue. Ethanol (200 mL) was addedto the oil. Combined stirring and cooling produced a crystalline solidcollected by vacuum filtration and dried to give 67.2 g (76%) of ayellow solid. Melting point=86.0°-89.0° C. IR (KBr) 2965, 1655, 1595,1310, 1135, 840, 770, 695 cm⁻¹. FDMS, m⁺ /z 338 (C₂₀ H₁₈ O₃ S). ¹ H NMR(CDCl₃) d 7.82 (m, 2H), 7.76 (d, 2H, J=8 Hz), 7.53 (m, 3H), 7.36 (d, 2H,J=8 Hz), 6.68 (d, 1H, J=3 Hz), 1.25 (d, 6H, J=7 Hz). Anal. Calcd. forC₂₀ H₁₈ O₃ S: C, 70.98;H, 5.36. Found: C, 70.63,H, 5.34.

Preparation of4H-1,1-Dioxo-2-(p-isopropylphenyl)-6-phenyl-4-(dicyanomethylidene)thiapyran:

A mixture of 67.2 grams (0.199 mol) of4H-1,1-Dioxo-2-(p-isopropylphenyl)-6-phenylthiapyran-4-one and 15.0 g(0.227 mol--a slight excess) of malononitrile in 110 mL ethanol washeated at reflux on a steam bath in a flask equipped with mechanicalstirring and a water-cooled condenser w/dry tube. To this mixture, asolution of 0.50 mL piperidine in 20 mL ethanol was added dropwise via apressure equalizing addition funnel. The reaction mixture refluxedapproximately 4 hours, during which time all solids gradually dissolvedand precipitated a yellow crystalline solid. The reaction mixture wascooled to ambient temperature and the product was collected by vacuumfiltration and washed with 100 mL ethanol. The solid was heated toboiling in ethyl acetate/ethanol, cooled to ambient temperature andvacuum filtered to give 50.0 grams (66% of theoretical yield) of abright yellow crystalline solid. Melting point=157.0°-159.0° C. IR (KBr)2980, 2225, 1305, 1140, 835, 770, 690 cm⁻¹. FDMS, m⁺ /z 386 (C₂₃ H₁₈ N₂O₂ S). ¹ H NMR (CDCl₃) d 7.82 (m, 4H) , 7.58 (m, 3H) , 7.40 (d, 2H, J=8Hz), 7.32 (d, 1H, J=2 Hz), 7.30 (d, 1H, J=2 Hz), 3.00 (septet, 1H, J=7Hz), 1.30 (d, 6H, J=7 Hz). Anal Calcd. for C₂₃ H₁₈ N₂ O₂ S: C, 71.48;H,4.69, N, 7.25. Found: C, 70.93;H, 4.82, N, 7.08.

Saturated solutions of the sulfone of this example were prepared intoluene and dichloromethane at ambient temperature (approx. 23° C.) todetermine maximum solubility. Results are presented in Table 1.

COMPARATIVE EXAMPLES A-C

Saturated solutions of PTS,4H-1,1-dioxo-2-(4-ethylphenyl)-6-(2-methylphenyl-4-(dicyanomethylidene)thiapyranand 4H-1,1-dioxo-2-(5-methylthienyl)-6-(4-ethylphenyl) (ComparativeExamples A, B, and C, respectively) were prepared in toluene anddichloromethane at ambient temperature (approx. 23° C.) to determinemaximum solubility. Results are presented in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Solubility of Sulfones (Saturated Solutions)                                                                  Maximum sulfone                               Example or Comparative Ex:      solubility                                    Compound                   Solvent                                                                            (wt/wt % at 23° C.)                    __________________________________________________________________________    Example 1:                 toluene                                                                            4.6                                            ##STR14##                                                                    Example 1:                 dichloro-                                                                          13.5                                           ##STR15##                 methane                                            Example 2:                 toluene                                                                            12                                             ##STR16##                                                                    Example 2:                 dichloro-                                                                          >15                                            ##STR17##                 methane                                            Comparative Example A: PTS toluene                                                                            2                                              ##STR18##                                                                    Comparative Example A: PTS dichloro-                                                                          6.5                                            ##STR19##                 methane                                            Comparative Example B      dichloro-                                                                          4.7                                            ##STR20##                 methane                                            Comparative Example C      dichloro-                                                                          4.7                                            ##STR21##                 methane                                            __________________________________________________________________________

EXAMPLES 3-5

In Examples 3-5, electrophotographic elements of the inventioncontaining the sulfone of Example 1: ##STR22## in the CTL were preparedby the following procedure:

A thin conductive layer of aluminum was vacuum-deposited on a 178μm-thick film of polyethylene terephthalate. The aluminum-coated filmwas then overcoated by electron-beam evaporation with a500-angstrom-thick layer of silicon dioxide prior to application of acharge-generation layer.

A charge-generation layer (CGL) was prepared by dispersing 2 parts byweight of titanyl tetrafluorophthalocyanine (described in U.S. Pat. No.4,701,396), a charge-generation material, in a solution of 1 part byweight of a polymeric binder, comprising a polyester formed from4,4'-(2-norbornylidene)diphenol and terephthalic acid-azelaic acid(40:60 molar ratio) in dichloromethane, ball milling the dispersion for60 hours, diluting with a mixture of dichloromethane and1,1,2-trichloroethane (final weight ratio ofdichloromethane:trichloroethane was 85:15) to achieve suitable coatingviscosity, coating the dispersion on the conductive layer, andevaporating the solvent to yield a CGL of 1.2 mm thickness.

A coating solution for forming a charge-transport layer (CTL) comprising10 weight percent solids in dichloromethane was then prepared. Thesolids comprised the sulfone of Example 1 and a polymeric bindercomprising a polyester formed from 4,4'-(2-norbornilidene) diphenol andterephthalic acid: azelaic acid (40:60 molar ratio). The sulfone ofExample 1 comprised 20, 30, and 40 weight percent (Examples 3, 4, 5,respectively) of the total of polymer binder and sulfone in the coatingsolution. The solution was then coated over the CGL using a 5 mil doctorblade to form the CTL on the CGL. The combined thickness of the CGL andCTL was about 5 to 10 μm.

Electrophotographic sensitivity of the elements so prepared wasdetermined by first electrostatically corona-charging each element to auniform initial positive potential, then exposing the elements to asimulated imaging exposure, that is, an exposure to actinic radiation(radiation having peak intensity at a wavelength to which thecharge-generation material in the elements is sensitive in order togenerate electron-hole pairs in the CGL) in amounts sufficient todischarge 50% and 80% of the initial voltage. Electrophotographicsensitivity was measured in terms of the amount of incident actinicradiant energy (expressed in ergs/cm²) needed to discharge the initialvoltage down to the desired level. The lower the amount of radiationneeded to achieve the desired degree of discharge, the higher is theelectrophotographic sensitivity of the element, and vice versa. Each ofthe uniformly charged elements was subjected to radiation at awavelength of about 830 nm, at a rate of about 2 ergs per cm² of elementsurface per second through the outer surface of the CTL, and thenmeasuring the values for 50% discharge (also referred to as "halfdischarge", "E(V_(o), 50%)", and "E(V_(o), 1/2)") and 80% discharge(also referred to as "E(V, 80%)").

Dark decay properties were determined by measuring the dark decay(expressed in volts/second), that is, the rate of dissipation of theinitial uniform voltage while the elements remained in darkness, i.e.,before any exposure to actinic radiation. This was accomplished by firstcorona charging in the same manner as in the above sensitivitymeasurements, followed by measuring the initial voltage and the voltageremaining in the element after 2 seconds in darkness and dividing thedifference by 2. The lower the rate of discharge in darkness, the betteris the dark decay property of the elements, i.e., the better theirability to retain their initial potential before exposure.

Results are presented in Table 2. "Charge transport agent wt %" refersto the percent by weight of electron-transport agent employed, based onthe total weight of polymeric binder and electron-transport agent,included in the solution used to coat the CTL of the element. "Darkdecay" refers to the rate of dark decay of the elements, prior toexposure to actinic radiation, measured in volts/second (V/s) asdescribed above. "E(V_(o) 50%)" refers to the amount of incident actinicradiant energy, expressed in ergs/cm², needed to discharge 50% of theinitial voltage, V_(o). "E(V_(o) 80%)" refers to the amount of actinicradiant energy needed to discharge 80% of V_(o).

Electron mobility was measured by the time-of-flight method as generallydiscussed in Borsenberger, P. M., and Weiss, D. S., OrganicPhotoreceptors for Imaging Systems, Marcel Dekker, Inc., New York, 1993,p. 279 and as described in more detail in U.S. Pat. No. 5,300,385 toDetty et al, except that the substrate electrode was aluminum and theCTL thickness ranged from 6.9 to 10.6 micrometers. In samples containing20 and 30 weight percent of the sulfone of Example 1 (Examples 3 and 4),the electron mobility was approximately the same as in samplescontaining equal weight percentages of PTS. For example, at a fieldstrength of 2×10⁵ V/cm, the mobility in Example 4 (a sample containing30 weight percent of the sulfone of Example 1) was 1.0×10⁻⁷ cm² /V.sec.This compares to a mobility of 0.6×10⁻⁷ cm² /V.sec for PTS at the samefield strength.

EXAMPLES 6-8

In Examples 6-8, the procedures of Examples 3-5 were repeated for thesulfone of Example 2: ##STR23## Results as to electrophotographicexposure for half discharge, 80% discharge, and dark decay werecomparable to the results for Examples 3-5.

COMPARATIVE EXAMPLES D-F

In Comparative Examples D-F, the procedures of Examples 3-5 werefollowed with the exception that the solids contained 20, 30, and 40weight percent PTS in place of the sulfone of Example 1.Electrophotographic exposure results are presented in Tables 2.

                  TABLE 2                                                         ______________________________________                                        Electrophotographic Exposure for Half Discharge, 80%                          Discharge, and Dark Decay for Examples 3-5 and                                Comparative Examples                                                                  Charge                                                                Ex. or  transport                    Dark                                     Comp.   agent    E(V.sub.o, 50%)                                                                           E(V.sub.o, 80%)                                                                       Decay                                    Ex.     wt %     ergs · cm.sup.-2                                                                 ergs · cm.sup.-2                                                             V/s                                      ______________________________________                                        Ex. 3   20%      9.1         43      3.0                                      Comp.   20%      8.2         33      3.2                                      Ex. D                                                                         Ex. 4   30%      7.3         28      2.4                                      Comp.   30%      6.9         26      3.9                                      Ex. E                                                                         Ex. 5   40%      6.5         21      2.2                                      Comp.   40%      6.5         23      2.2                                      Ex. F                                                                         ______________________________________                                    

EXAMPLES 9a-9g and 10a-10g

Electrophotographic elements were prepared in substantially the samemanner as in Examples 3-5, with the exception that Examples 9a-9g eachused as charge transport agent: ##STR24## and Examples 10a-10g each usedas charge transport agent: ##STR25##

The relative concentrations of charge transport agent and binder (inparts by weight) were varied as indicated in Table 3. Each element wasexamined to determine the extent of crystallization of the chargetransport agent in the element. Crystallization visible withoutmagnification extending over less than 5 percent of the element wasconsidered acceptable. Visible crystallization extending over more than5 percent of the element was considered unacceptable. Results arepresented in Table 3.

COMPARATIVE EXAMPLES G1-G7

The procedures of Examples 9a-9g and 10a-10g were followed except PTSwas substituted for the indicated sulfones. Results are presented inTable 3.

                  TABLE 3                                                         ______________________________________                                                    ACCEPTABLE COMPATIBILITY                                                      OF CHARGE TRANSPORT AGENT                                                     AND BINDER IN ELECTROPHO-                                                     TOGRAPHIC ELEMENT                                                 SULFONE:BINDER                                                                              Comparative                                                     RATIO (Wt. %/Wt. %)                                                                         Examples G Examples 9                                                                              Example 10                                 ______________________________________                                        60/40         G1: YES    9a: YES   10a: YES                                   65/35         G2: YES    9b: YES   10b: YES                                   70/30         G3: NO     9c: YES   10c: YES                                   75/25         G4: NO     9d: YES   10d: YES                                   80/20         G5: NO     9e: NO    10e: YES                                   85/15         G6: NO     9f: NO    10f: YES                                   90/10         G7: NO     9g: NO    10g: NO                                    ______________________________________                                    

Tables 1 and 3 illustrate the surprising nature of the solubility andcompatibility characteristics of the sulfones of the invention.Solubilities vary greatly between the compounds of the indicatedExamples and Comparative Examples despite what would otherwise appear tobe minor differences in chemical structure. Table 2 illustrates thatelements including the sulfones of the invention haveelectrophotographic characteristics, including dark decay andsensitivity, at least comparable to PTS. Examples 1-2 and 9-10illustrate the very high charge transport agent loading possible withthe sulfones of the invention.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it should be appreciated thatvariations and modifications can be effected within the spirit and scopeof the invention.

What is claimed is:
 1. A multilayered electrophotographic elementwherein at least one of said layers includes polymeric binder and acharge transport agent having the general structure ##STR26## wherein Ris selected from the group consisting of alkyl and cycloalkly groupshaving from 1 to about 10 carbons, aryl and heteroaryl groups having atotal of carbons and heteroatoms of from 6 to about 12, a furyl group, aselenophene group, and a thienyl group; and T is alkyl having from 1 to4 carbons.
 2. The electrophotographic element of claim 1 wherein saidcharge transport agent is more compatible with said polymeric binderthan is 4-dicyanomethylene-2-p-tolyl-6-phenyl-4H-thiopyran-1,1-dioxide.3. The electrophotographic element of claim 2 wherein said chargetransport agent is from about 20 to 70 weight percent of the total ofsaid charge transport agent and said polymeric binder.
 4. Theelectrophotographic element of claim 1 wherein R is an aryl orheteroaryl group having a total of carbons and heteroatoms of from 6 toabout 12 and T is alkyl having from 1 to 4 carbons.
 5. Theelectrophotographic element of claim 1 wherein said polymeric binder isselected from the group consisting of styrene-butadiene copolymers;vinyltoluene-styrene copolymers; styrene-alkyd resins; silicone-alkydresins; soya-alkyd resins; vinylidene chloride-vinyl chloridecopolymers; poly(vinylidene chloride); vinylidene chloride-acrylonitrilecopolymers; vinyl acetate-vinyl chloride copolymers; poly(vinylacetals); nitrated polystyrene; poly(methylstyrene); isobutylenepolymers; polyesters; phenol-formaldehyde resins; ketone resins;polyamides; polycarbonates; polythiocarbonates;poly-[ethylene-co-isopropylidene-2,2-bis(ethyleneoxy-phenylene)terephthalate];copolymers of vinyl haloacrylates and vinyl acetate; chlorinatedpolyolefins; and polyimides.
 6. The electrophotographic element of claim1 wherein T is methyl or ethyl.
 7. The electrophotographic element ofclaim 1 wherein R is phenyl or thienyl.
 8. The electrophotographicelement of claim 1 wherein said charge transport agent is selected fromthe group consisting of ##STR27##
 9. The electrophotographic element ofclaim 1 further characterized as having one layer having the primaryfunction of charge generation and having another layer having theprimary function of charge transport.
 10. An electrophotographic elementcomprising an electrically conductive layer, a charge generating layer,and a layer including a polymeric binder and a charge transport agenthaving the general structure ##STR28## wherein R is selected from thegroup consisting of aryl and heteroaryl groups having a total of carbonsand heteroatoms of from 6 to about 12, a furyl group, a selenophenegroup and a thienyl group; and T is alkyl having from 1 to 4 carbons.11. The electrophotographic element of claim 10 wherein said layerincluding said charge transport agent further includes a polymericbinder and said charge transport agent is greater than 50 weight percentof the total of said charge transport agent and said polymeric binderand said layer is substantially free of zones of incompatibility. 12.The electrophotographic element of claim 11 wherein said layer includingsaid charge transport agent further includes a polymeric binder and saidcharge transport agent is more compatible with said polymeric binderthan is 4-dicyanomethylene-2-p-tolyl-6-phenyl-4H-thiopyran-1,1-dioxideand said polymeric binder is selected from the group consisting ofstyrene-butadiene copolymers; vinyltoluene-styrene copolymers;styrene-alkyd resins; silicone-alkyd resins; soya-alkyd resins;vinylidene chloride-vinyl chloride copolymers; poly(vinylidenechloride); vinylidene chloride-acrylonitrile copolymers; vinylacetate-vinyl chloride copolymers; poly(vinyl acetals); nitratedpolystyrene; poly(methylstyrene); isobutylene polymers; polyesters;phenol-formaldehyde resins; ketone resins; polyamides; polycarbonates;polythiocarbonates;poly-[ethylene-co-isopropylidene-2,2-bis(ethyleneoxy-phenylene)terephthalate];copolymers of vinyl haloacrylates and vinyl acetate; chlorinatedpolyolefins; and polyimides.
 13. The electrophotographic element ofclaim 12, wherein R is phenyl or thienyl.
 14. The electrophotographicelement of claim 13 wherein T is methyl or ethyl.
 15. Anelectrophotographic element comprising in a polymeric binder a compoundhaving the structure ##STR29## wherein R is substituted or unsubstitutedand is selected from the group consisting of alkyl and cycloalkyl groupshaving from 1 to about 10 carbons, aryl and heteroaryl groups having atotal of carbons and heteroatoms of from 6 to about 12, a furyl group, aselenophene group, and a thienyl group; and T is alkyl having from 1 to4 carbons.
 16. The electrophotographic element of claim 15 wherein T ismethyl or ethyl.
 17. The electrophotographic element of claim 15 whereinR is phenyl or thienyl.
 18. The electrophotographic element of claim 15wherein said charge transport agent is selected from the groupconsisting of ##STR30##
 19. The electrophotographic element of claim 15wherein R is selected from the group consisting of a furyl group, aselenophene group and thienyl group.
 20. The electrophotographic elementof claim 15 wherein R is substituted by alkyl having from 1 to about 12carbons, alkoxy having from 1 to about 12 carbons, nitro, cyano,dialkylamino, arylalkylamino or diarylamine.